1. Field of the Invention
This invention relates to the field of laser instruments and more particularly to the field of systems used to control and to peak the response of a laser signal source such as the signal output from a ring laser gyro.
2. Prior Art
Pathlength control assemblies typically have a frame or body with a flat mounting surface on which a multi-layer dielectric mirror is centrally formed. The flat surface is typically bonded to an end or corner of an optical cavity in a laser or ring laser gyro body to reflect light passing through the cavity incident on the mirrored surface. The mirrored surface is typically formed on thin wall that serves as a diaphragm to permit slight motion of the mirrored surface within the cavity. A PZT (piezoelectric transducer) is driven with an electrical control signal to move the diaphragm to thereby shorten or lengthen the optical pathlength to optimize the resonance of the cavity. The diaphragm surface is mechanically coupled by a link or a rod to a surface on the opposite side of the frame or body that is displaced by the piezoelectric transducer.
Configurations of this type typically exhibit hysteresis that is inherent in the material from which the PZT devices are made. A control signal of a first amplitude to the PZT will produce a first deflection that will not be matched by an equivalent deflection in the opposite direction by removal of the signal and reapplication of a signal of equal value and opposite polarity to the PZT. A signal of opposite polarity and larger amplitude is required to overcome the hysteresis in the PZT. Therefore; the drive signal to the PZT device is not linearly related to the deflection of the mirror surface in such prior art pathlength control devices.